Firefighting has been identified as a high-risk occupation for traumatic injuries by the National Occupational Research Agenda (NORA) Traumatic Injury Team as firefighters (FF) routinely performing physically strenuous work in heavy, constricting clothing and often in hot and hostile environments. Individually, each of these factors place great strain on the cardiovascular (CV) system. Combined, they contribute to FFs having the highest rate of occupational fatalities due to heart attacks. It is known that myocardial infarctions (MIs) account for nearly 50% of line of duty deaths in FF, but we do not know the mechanisms by which MIs occur nor do we understand the effect of on-scene interventions in mitigating heat stress or CV strain, which can lead to MIs. This study will examine how physically taxing firefighting tasks influence key hemostatic variables and how on scene rehabilitation (OSR) interventions impact these measures. Specifically, this initial study will investigate the effect of firefighting on body temperature, platelet function, procoagulatory, anticoagulatory, profibrinolytic, and antifibrinolytic markers, and will document the extent to which these variables recover within 2 hours. Subjects will participate in two separate trials that will differ only in the OSR component, thus permitting researchers to examine the effect of OSR on body temperature, hemostasis, and psycho-physiological variables as well as on subsequent physical and psychological performance. This study will provide important scientific information regarding the effect of firefighting on the hemostatic system and will provide practical information on the effectiveness of OSR to lessen dangerous heat stress conditions, mitigate CV strain, and improve FF performance. OSR is widely recommended, yet to date there is no scientific study that documents the efficacy of FF OSR or that differentiates the effectiveness of different strategies. As FFs are routinely called upon to rescue citizens from danger, the health and performance of this occupational group has a significant effect on public health. Additionally, rehabilitation interventions developed from this initial study and future studies may be useful for other occupations involving work in conditions of high heat stress. Interventions that are effective for FF will find application in other occupations that face high heat stress or multiple stressors in a manner similar to the way that sports drinks designed for athletes have been found to benefit occupations such as construction and mining. [unreadable] [unreadable] [unreadable]